Cruz-Díaz, Alvin O.

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    Design and characterization of a pressure differential trapping mechanism for suspended micro-particles in a micro-fluidic device
    (2012) Cruz-Díaz, Alvin O.; Díaz-Rivera, Rubén E.; College of Engineering; Quintero, Pedro; Valentín, Ricky; Department of Mechanical Engineering; Camayd, Elvia
    The increasing interest for dedicated analysis of single particles at microscopic scales, such as biological cells, has led researchers to create micro-fluidic systems capable of trapping particles in a liquid flow. The present study tests a device that employs a pressure difference trapping mechanism to isolate suspended micro-particles. The studied microfluidic device was fabricated using typical soft lithography and consists of parallel canals that are linked by small apertures that function as localized pressure-gradient traps. Experiments to characterize the functionality of the trapping sites of the device were conducted using polystyrene beads. These experiments consisted of using 20 µm polystyrene beads suspended in PBS, which were introduce using a syringe pump, while one outlet port of the device was controlled to produce an outflow rate of 25%, 50%, 62.5% and 75% of the inflow rate. Another case in which the outlet remained at atmospheric pressure was also studied. The experiments performed with 20 µm beads demonstrated that the apertures were capable of trapping and retaining the beads. A micro-PIV was used to characterize the flow and the velocity profile in different parts of the device. The results from the micro-PIV experiments were used to validate a computational fluid dynamics model using COMSOL Multiphysics. The experiments show that the trapping efficiency is a strong function of the controlled output flow suggesting that the functionality of the device could be manipulated with a variable fluidic resistance. It was also found that the velocity profile of the computational model agrees well with experiments carried out with the micro-PIV, but only when there is slip at the PDMS walls. We suspect that the velocity slip is due to the surface treatment of the microchannel walls (air plasma followed by bovine serum albumin functionalization). However, the evidence is not conclusive. The validated computational model presented in this study will serve as a stepping stone for the development of high-density cell isolation micro-devices for high-throughput single-cell electroporation applications and the detection of circulating tumor cells.